During printing operations, a web to be printed moves under tension and at high speed on the or each printing and feed cylinder.
The or each printing and feed cylinder is in contact with the web and is driven in rotation in such a manner that it contributes to the feeding of the web. The or each printing and feed cylinder also prints an image on the web by depositing ink thereon.
In the event of the web breaking downstream of a printing unit, the web loses its tension and tends to adhere to the or each printing and feed cylinder of the printing unit owing to the ink covering said cylinder. There is thus a risk that the web will become wound around a printing cylinder, which may very rapidly damage the printing cylinder, and more generally the printing unit, owing to an accumulation of layers of web between cylinders of the printing unit.
The replacement of a printing cylinder and the return of a printing unit to a working condition are extremely expensive operations.